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Electrochem 2020, 1 243 The utility of high sulfur-content materials prepared via inverse vulcanization for Li-S batteries has been so hotly pursued recently that the area was recently reviewed [95]. Since that review, however, other reports have emerged. One example [96] employs poly(sulfur-co-1-vinyl-3-allylimidazolium bromide) made by inverse vulcanization of S8 with an ionic polymer. The dual role of this material as cathode and polysulfide suppression material was demonstrated and supported by DFT calculations Electrochem 2020, 2, FOR PEER REVIEW 19 as well. The cell employing this cathode retained over 90% of its initial capacity even after 900 cycles. 4.4. Semiconducting, Hyperbranched and Inert Polymer Supports and Separators 4.4. Semiconducting, Hyperbranched and Inert Polymer Supports and Separators An approach to preparing flexible batteries [97,98] is to employ organic semiconducting An approach to preparing flexible batteries [97,98] is to employ organic semiconducting polymers polymers such as polyaniline (PANI, Figure 15) as a component of the conducting layers [64]. When such as polyaniline (PANI, Figure 15) as a component of the conducting layers [64]. When MnO2 MnO2 nanoparticles are embedded in PANI, a porous network forms that can be used as a scaffold nanoparticles are embedded in PANI, a porous network forms that can be used as a scaffold for the for the sulfur cathode. Scaffolding reduces volume changes associated with unsupported sulfur sulfur cathode. Scaffolding reduces volume changes associated with unsupported sulfur cathodes. cathodes. A synergistic result of the channels provided by the scaffolding material is that the channels A synergistic result of the channels provided by the scaffolding material is that the channels improve improve transport of ions and carrier species through the electrode as well. The chemical composition transport of ions and carrier species through the electrode as well. The chemical composition of of the scaffold to include a semiconducting polymer also facilitates conversion of polysulfide species the scaffold to include a semiconducting polymer also facilitates conversion of polysulfide species to thiosulfates. This in-cathode chemical reactivity should significantly attenuate the shuttle effect. to thiosulfates. This in-cathode chemical reactivity should significantly attenuate the shuttle effect. The initial study on a Li-S battery employing this scaffolded cathode displayed stable capacity as The initial study on a Li-S battery employing this scaffolded cathode displayed stable capacity as high as 1195 mA h g−1 at 0.5 C even after 100 cycles. A discharge capacity of 640 mA h g−1 at 2 C was high as 1195 mAh g −1 at 0.5 C even after 100 cycles. A discharge capacity of 640 mAh g −1 at 2 C was achievable even after 500 cycles with this configuration. achievable even after 500 cycles with this configuration. H HN Nnn Figure 15. Chemical structures of polyaniline (PANI) and polypyrrole (PPyr). Figure 15. Chemical structures of polyaniline (PANI) and polypyrrole (PPyr). Another effort to combine the conductivity of an organic semiconducting polymer with a metal Another effort to combine the conductivity of an organic semiconducting polymer with a metal oxide employed polypyrrole (PPyr, Figure 15) and tin oxide nanoparticles [65]. The use of polypyrrole oxide employed polypyrrole (PPyr, Figure 15) and tin oxide nanoparticles [65]. The use of indeed improved the conductivity of the cathode and effectively hindered polysulfide diffusion due to polypyrrole indeed improved the conductivity of the cathode and effectively hindered polysulfide the polarity of the backbone structure. The tin oxide particles also served to trap polysulfides through diffusion due to the polarity of the backbone structure. The tin oxide particles also served to trap covalent bond formation. A cell fabricated to include ~65 wt % sulfur in the cathode was operated polysulfides through covalent bond formation. A cell fabricated to include ~65 wt% sulfur in the for 500 cycles (1 C) and exhibited a capacity loss of only 0.05%/cycle. At higher current density (5 C) cathode was operated for 500 cycles (1 C) and exhibited a capacity loss of only 0.05%/cycle. At higher 383.7 mAh/g at 5 C was attainable with coulombic exceeding 90%. current density (5 C) 383.7 mA h/g at 5 C was attainable with coulombic exceeding 90%. Polypyrrole can also be incorporated by in situ polymerization within a mesoporous silica Polypyrrole can also be incorporated by in situ polymerization within a mesoporous silica framework having NiO nanoparticles dispersed in it [66]. This mesoporous material effectively framework having NiO nanoparticles dispersed in it [66]. This mesoporous material effectively provides physical trapping of polysulfide species as they migrate through it as well as formation provides physical trapping of polysulfide species as they migrate through it as well as formation of of chemical bonds to the polysulfide species. A high capacity stability is affected by this material, chemical bonds to the polysulfide species. A high capacity stability is affected by this material, and and even after 300 cycles the capacity holds at ≥700 mA−1h g−1. evenafter300cyclesthecapacityholdsat≥700mAhg . Semiconducting poly(N-methylpyrrole) can also be used in conjunction with S@reduced graphene Semiconducting poly(N-methylpyrrole) can also be used in conjunction with S@reduced oxide [99]. A recent application of this composite was in conjunction with a polymer gel electrolyte graphene oxide [99]. A recent application of this composite was in conjunction with a polymer gel fabricated by combining silica nanoparticles with lithium imide and poly(methyl methacrylate). electrolyte fabricated by combining silica nanoparticles with lithium imide and poly(methyl The intimate contact between the polypyrrole derivative and the gel electrolyte provides outstanding Li methacrylate). The intimate contact between the polypyrrole derivative and the gel electrolyte ions exchange between layers and the Li ion diffusion coefficient can be as high as 10−6 cm2 s−1. The high provides outstanding Li ions exchange between layers and the Li ion diffusion coefficient can be as lithiumion−6cond2uc−1tivityisaccompaniedbycommensuratelylowpolysulfidespeciespermittivity high as 10 cm s . The high lithium ion conductivity is accompanied by commensurately low through the material. This is manifest in device performance, wherein the capacity retention after polysulfide species permittivity through the material. This is manifest in device performance, 500 cycles is 3-fold higher when the gel electrolyte is used compared to traditional organic electrolytes. wherein the capacity retention after 500 cycles is 3-fold higher when the gel electrolyte is used The use of gel electrolytes, fire-retardant electrolytes and solid-state electrolytes have all shown great compared to traditional organic electrolytes. The use of gel electrolytes, fire-retardant electrolytes promise in solving some safety issues and alleviating the shuttle effect in recent work in the field. and solid-state electrolytes have all shown great promise in solving some safety issues and alleviating the shuttle effect in recent work in the field. Earlier studies suggested that hyperbranched polymers, such as those prepared by inverse vulcanization [63] may also prove effective as cathode support materials in Li-S batteries [100]. Recently, a polymer-encapsulated sulfur cathode strategy [67] thus used HPEIGA, a readily- synthesized hyperbranched material prepared from polyethyleneimine and glutaraldehyde. The hyperbranched material serves the dual role of having low permeability to polysulfide species duePDF Image | Lithium-Sulfur Batteries: Advances and Trends
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